Clustering in artificial categories: An equivalence analysis

Category clustering is a robust finding in the free recall of familiar cate gory members, but has rarely been studied with artificial categories. In th e present study, college students learned artificial categories via stimulu s-equivalence methodology. Arbitrary match-to-sample training with nonsense syllables established three interrelated conditional discriminations, and, for most subjects, unreinforced test trials revealed the emergent stimulus -control relations considered to be evidence of equivalence classes. Free-r ecall tests revealed evidence of significant within-class clustering both b efore and after equivalence testing, but was more pronounced after the equi valence tests. These findings confirm that classic phenomena like clusterin g in free recall can be studied with stimulus-equivalence methodology, thus allowing for experimental control over relevant variables.